3GPP Long Term Evolution (LTE) is a standard for mobile phone network technology. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS), and is a technology for realizing high-speed packet-based communication that can reach high data rates on both downlink and uplink channels. As illustrated in FIG. 1, LTE transmissions are sent from base stations 102, such as Node Bs (NBs) and evolved Node Bs (eNBs) in a telecommunications network 104, to mobile stations 106,108 (e.g., user equipment (UE)).
The LTE standard is primarily based on Orthogonal Frequency Division Multiplexing (OFDM) in the downlink, which splits the signal into multiple parallel sub-carriers in frequency, and Single Carrier Frequency Domain Multiple Access (SC-FDMA) in the uplink.
As illustrated in FIG. 2, a sub-frame 200 may be transmitted in accordance with the LTE standard, and may consists of 12 or 14 sub-carriers 204 in the frequency domain. In the time domain, the sub-frame may be divided into a number of OFDM (or SC-FDMA) symbols 208. An OFDM (or SC-FDMA) symbol 208 may include a cyclic prefix 206. A unit of one sub-carrier and one symbol is referred to as a resource element (RE) 202. Thus, a sub-frame may consist of, for example, 84 REs in a 12×7 configuration as shown in FIG. 2.
Currently, LTE does not support dedicated data channels; rather, shared channel resources are used in both the downlink and uplink transmissions. These shared resources, Downlink Shared Channel (DL-SCH) and Uplink Shared Channel (UL-SCH), are each controlled by a single scheduler that assigns different parts of the downlink and uplink shared channels to different scheduling entities (e.g., UEs) for reception and transmission, respectively. These schedulers are in full control of in which sub-frame a UE should receive on DL-SCH, or is allowed to transmit on UL-SCH. Scheduling decisions are sent to each UE as downlink assignments and uplink grants. Downlink assignment information and uplink grants may be transmitted as Downlink Control Information (DCI), for instance, using L1/L2 control signaling.
For an uplink (UL) transmission, the portion of the bandwidth assigned to one UE is always a set of contiguous scheduling blocks (SBs) due to the single carrier constraint imposed by the SC-FDMA transmission scheme. These assigned bandwidth resources are indicated in the DCI by a start-SB and an allocation size, which is provided as a number of SBs. LTE currently supports full dynamic scheduling; therefore, the particular bandwidth resource assignment to a UE is only valid for one sub-frame. In the next sub-frame, the same bandwidth resources may be re-assigned, for instance, to another UE.
An exemplary UL scheduling result for three scheduling entities is provided in FIG. 3. The three sub-frames 302 illustrate potential scheduling results that are possible using dynamic scheduling. For instance, multiple users may share different parts of the available frequency resources within a single sub-frame, as shown by sub-frame n. Alternatively, all of the frequency resources of a sub-frame may be assigned to one user (sub-frame n+1). Similarly, no users are allocated any frequency resources within sub-frame n+2. In the illustration of FIG. 3, the available bandwidth is reduced by four SBs 304 in each sub-frame, which are occupied by uplink L1/L2 control signaling.
Presently, resource allocation depends on the properties of the user population in the system, e.g., the number of users, their traffic models and radio channel characteristics, as well as the algorithm implementing the scheduling functionality. The strategy that defines the manner in which resources in the time and frequency domains are allocated to a set of users is commonly referred to as a scheduling algorithm.
Scheduling strategies may be accomplished by scheduling algorithms in either the time domain or frequency domain. Time domain scheduling strategies include, for example, Round Robin, Proportional Fair, or delay based. Frequency domain scheduling strategies may include Resource Fair and Frequency Selective scheduling. For instance, allocation may be optimized based on knowledge of the candidate UEs or known channel quality parameters, where devices with low channel quality may receive a larger allocation.
Certain scheduling algorithms are tailored to maximize spectrum efficiency independent of end user behavior, such as the end user's Quality of Service (QoS) class, the traffic model, etc. In a typically system, there may be many users with varied traffic properties. For instance, some users have little data to transmit, while some users are limited by their maximum transmit power in the uplink. These users cannot fully utilize the spectrum with high efficiency.
For users that have both a full buffer of transmit data and good radio conditions, acceptable spectrum utilization and efficiency can be achieved based on present technologies. However, there is a need for systems and methods to schedule different types of users with varied amounts of data and transmission properties such that both high spectrum efficiency and good end-user performance may be achieved.